mini-Neptunes Archives - Page 2 of 4 - Astrobiology

A classification scheme for volatile-rich sub-Neptunes. The schematic compares different types of sub-Neptunes with H2 and H2O dominated atmospheres as a function of the equilibrium temperature and H2 content. Ice worlds: Cold subNeptunes where any water is frozen in a layer of ice atop high-pressure ice, with a thin H2-dominated atmosphere (65). Hycean worlds: Warmer than ice worlds, hycean worlds have a thin H2-rich atmosphere overlying an ocean of liquid water, which itself is above a layer of high-pressure ices. These planets have the potential to support habitable conditions (9). Mini-Neptunes: Sub-Neptunes with a deep H2-rich atmosphere followed by a mixed H2O-H2 supercritical layer below before reaching a layer of high-pressure ice and then a core (17, 65). Steam worlds: Water worlds with H2O dominated atmospheres. At equilibrium temperatures above Tcrit, a high proportion of H2O exists in the atmosphere, with a supercritical mixed-envelope at higher pressures. Supercritical mini-Neptunes: These planets are hotter than Tcrit, and contain interiors where H2 gas is highly soluble in supercritical H2O (46, 65). This mixed-envelope would lie over a layer of high-pressure ice above the core. Legend: The legend at the top shows the different compositions corresponding to the colors in the schematic, including the core, different phases of H2O and envelope composition; high-P ice refers to high-pressure ice. Note that the core has further distinct layers but we do not label them here. Sharp phase transitions are shown for ice-atmosphere and ocean-atmosphere transitions. Other phase transitions are marked by a gradient, as they may not be sharp phase transitions (83). -- astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report

Exploring The Sub-Neptune Frontier With JWST

by Keith CowingSeptember 25, 2025September 25, 2025

Sub-Neptune planets, with sizes and masses between those of Earth and Neptune, dominate the exoplanet population.

Diverse density and composition of small exoplanets. The plot shows M-dwarf planets that have precision mass and radius measurements (Luque & Palle´ 2022). Small planets of FGK stars also occupy a broad parameter space that spans from Earth composition to water worlds or planets with massive H/He envelopes (Parc et al. 2024). The planets in the 1.4 – 2.6 Earth’s radius range can be large rocky planets, water worlds, or having massive H/He envelopes (Luque & Palle´ 2022; Rogers et al. 2023). The figure is adapted from Rogers et al. (2023) with permission. -- astro-ph.IM

Astronomy & Telescopes, Atmospheres, Climate, Weather, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Status Report

Identifying Rocky Planets And Water Worlds Among Sub-Neptune-sized Exoplanets With The Habitable Worlds Observatory

by Keith CowingSeptember 23, 2025September 23, 2025

Astronomers are debating whether the plentiful “sub-Neptune” exoplanets — worlds a bit larger than Earth but smaller than Neptune — are predominantly rocky planets, water-rich “ocean worlds,” or gas-enshrouded mini-Neptunes.

Logarithm of exomoon lifetime (log10 (𝑡max ); color coded) from stability simulations that vary a host planet’s mass, tidal constant time-lag, 𝜏p, and initial eccentricity while using Earth-like parameters for the 𝑘2 Love number and moment of inertia constant, 𝐶. -- astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Status Report, Water/Hycean Worlds & Oceanography

Can Moons Exist Around The Habitable-zone Planet K2-18 b?

by Keith CowingJuly 18, 2025July 18, 2025

K2-18 b closely orbits a nearby M3 dwarf within its habitable zone, where this planet could be either a super-Earth or a mini-Neptune.

Distribution of 339 planets in the stellar effective flux (𝑆eff) versus stellar temperature (𝑇eff) space. Red solid circles indicate the 17 planets orbiting within the EHZ, while gray points depict the remaining planets. Solar system planets are marked with purple circles. The green solid lines correspond to the inner and outer edges of the classical 1D habitable zone, as defined by Kopparapu et al. (2013). The blue dashed line represents the inner edge of the Extended Habitable Zone (EHZ) around M dwarf stars, assuming 30% heat transport efficiency (Wandel 2023a). The brown curve marks the outer edge of the EHZ, determined by the melting of ice sheets driven by geothermal heat (Wandel 2023b). The gray dashed line indicates the tidally locked radius around M dwarf stars. The green shaded region defines the classical HZ and the blue shaded region highlights the extended HZ for tidally locked exoplanets. -- astro-ph.EP

Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Gaia - Planetary Perspectives, Habitable Zones, Imaging & Spectroscopy, Status Report, Water/Hycean Worlds & Oceanography

Exploring The Habitability And Interior Composition Of Exoplanets Lying Within The Extended Habitable Zone

by Keith CowingJuly 8, 2025July 8, 2025

Studying the habitability, internal structure and composition of exoplanets is crucial for understanding their potential to sustain life beyond our solar system.

Mass-Radius plot of asteroids, moons, planets, brown dwarfs and low-mass stars. From nearly 5600 exoplanets listed in the PHL-HWC database, 1504 are categorized as terrestrial worlds (orange dots), 2609 as Neptunian worlds (green dots), 1355 as Jovian worlds (purple dots), and 115 as brown dwarfs (brown dots). -- astro-ph.EP

Astrogeology, Atmospheres, Climate, Weather, Brown Dwarfs, Exoplanets, -moons, -comets, Gas Giants, Ice Giant, Nomenclature, Systematics, Natural History, Status Report

(Re)-Defining Planets — the Fundamental Plane of Planets

by Keith CowingJune 23, 2025June 23, 2025

6000+ exoplanets are now detected using various techniques, with estimates of billions of planets existing in our Galaxy alone.

Exoplanets - NASA Astrobiology

Astronomy & Telescopes, Exoplanets, -moons, -comets, Habitable Zones, Ice Giant, Status Report

Research On Super-Earths And Mini-Neptunes Suggests More Earth-like Planets May Exist

by Keith CowingMarch 24, 2025May 12, 2025

A new study by Rice University researchers Sho Shibata and Andre Izidoro presents a compelling new model for the formation of super-Earths and mini-Neptunes — planets that are 1 to […]

Snapshots show planetary seeds’ growth and migration from two rings of material. This simulation comes from our M6T2 scenario. The top-left panel shows the starting time of the simulation. The time of each snapshot is shown on the bottom-left of each panel. The color of each dot corresponds to the water mass fraction of each planetary seed. We plot planetesimal and pebble isolation masses with dotted and dashed lines, respectively. The planetesimal isolation mass is obtained by extrapolating the initial surface density of the inner planetesimal disk. The vertical blue dashed line shows the location of the water condensation line. The blue solid line is the boundary of the inward and outward migration where the migration torque is zero. -- astro-ph.EP

Exoplanets, -moons, -comets, Habitable Zones, Icy Worlds, Status Report, Water/Hycean Worlds & Oceanography

Formation of Super-Earths and Mini-Neptunes From Rings of Planetesimals

by Keith CowingJanuary 8, 2025

The solar system planetary architecture has been proposed to be consistent with the terrestrial and giant planets forming from material rings at ~1 au and ~5 au, respectively.

TESS aperture field around the target star TOI-1803. (Image generated with tpfplotter, Aller et al. (2020)). -- astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report

A Joint Effort To Discover And Characterize Two Resonant Mini Neptunes Around TOI-1803 With TESS, HARPS-N And CHEOPS

by Keith CowingDecember 16, 2024December 16, 2024

We present the discovery of two mini Neptunes near a 2:1 orbital resonance configuration orbiting the K0 star TOI-1803. We describe their orbital architecture in detail and suggest some possible […]

LEFT Panel: Contrast curves obtained from Gemini North ‘Alopeke and Gemini South Zorro instruments. Insets showcase 832 nm reconstructed images, highlighting the increased contrasts achieved with Zorro on Gemini South due to better seeing conditions and a longer total integration time. No close companion star was detected within the achieved 5σ magnitude contrast curves and angular limits from the 8-m diffraction limit out to 1.2 ′′. At the distance of TOI-4364, these limits correspond to spatial separations ranging from 0.88 − 52.8 AU. RIGHT Panel: SOAR sensitivity curve taken on October 18, 2021. The 5σ sensitivity limits are shown out to 3.15′′, corresponding to a projected separation of 138.1 AU. -- astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Status Report

TESS Hunt for Young and Maturing Exoplanets (THYME) XII: A Young Mini-Neptune on the Upper Edge of the Radius Valley in the Hyades Cluster

by Keith CowingOctober 17, 2024September 18, 2025

We present the discovery and characterization of TOI-4364 b, a young mini-Neptune in the tidal tails of the Hyades cluster, identified through TESS transit observations and ground-based follow-up photometry.

Mean−subtracted RV data plotted in gray dotted points for each of the HARPS (top panel), ESPRESSO (middle panel), and PFS (bottom panel) instruments, along with separate model curves for the planet model (blue solid line), the GP model (green solid line) and the full planet + GP model (magenta solid line). The error bars include the jitter component 𝜎 for each instrument, which was added in quadrature to the RV error for each data point. -- astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report

TOI-757 b: An Eccentric Transiting Mini-Neptune On Aa 17.5-d Orbit

by Keith CowingAugust 12, 2024August 10, 2024

We report the spectroscopic confirmation and fundamental properties of TOI-757 b, a mini-Neptune on a 17.5-day orbit transiting a bright star (V=9.7 mag) discovered by the TESS mission. We acquired […]